The research supported by this grant explores genetic and biochemical aspects of an enzyme system, steroid sulfatase. A genetic locus controlling this enzyme is located on the human X chromosome. Work in progress indicates that it may be the first biochemically defined marker to be assigned to the short arm of the human X. Furthermore, this locus may not be subject to "Lyonization", the process which functionally inactivates most other portions of one of the two X-chromosomes in normal female cells. A genetic deficiency of steroid sulfatase activity has been recognized in man and is responsible for abnormal steroid metabolism during fetal life leading to delayed onset of parturition. In addition, affected individuals experience a skin disease, ichthyosis, after birth. The mechanism of this dermatologic disease is being explored through the study of sulfated steroids and sterols in skin, and by investigating keratin production and degradation in cultured epidermal cells.